This invention relates to a group of receptor active compounds, primarily adrenergically active, and more particularly to compounds that contain a guanidino group or an amidino group.
It has previously been recognized that a variety of guanidine derivatives have alpha-adrenergic receptor activity in vivo. A variety of guanidine derivatives have also been used clinically as anti-hypertensive agents, including clonidine, guanabenz, guanacline, guanadrel, guanazodine, guanethidine, guanfacine and guanochlor, guanoxabenz and guanoxan.
There has recently been interest in the treatment of severe spinal trauma. The treatment has resulted in reduction of the ensuing spasticity in human, and in many spinal cord injured mammals. It has also resulted in partial or complete recovery of sensory-motor control below the trauma level. Publications by the present inventor and by others, confirming by independent tests the inventor""s results with the use of clonidine, a known alpha2-adrenoceptor agonist, include, for example: xe2x80x9cFunctional Restoration of the Traumatically Injured Spinal Cord in Cats by Clonidinexe2x80x9d, Naftchi, N. E., SCIENCE 217, pages 1042-1044 (1982); THE PHYSIOLOGIST, Volume 27, page 220, August, 1984, xe2x80x9cHistochemical Correlates Of Behavioral Effect of Alpha-2 Adrenergic Agonist in Spinal Ratsxe2x80x9d, N. E. Naftchi, et al, and a more complete text provided in a paper given at the American Congress For Rehabilitation Medicine, 61st Annual Session, Oct. 23, 1984, xe2x80x9cNewer Research in Spinal Cord Injury, Mechanism and Prevention of Acute Spinal Cord Injuryxe2x80x9d xe2x80x9cTreatment of Mammalian Spinal Cord Injury With Antioxidantsxe2x80x9d, by N. Eric Naftchi, INT. J. DEVL. NEUROSCIENCE, vol. 9, No. 2, pp 113-126 (1991).
Clonidine and guanabenz, both alpha2-adrenergic receptor agonists used in the earlier work, had limited usefulness because long-term treatment with these two agents resulted in the sedation, sleepiness and desensitization of the subjects. In addition to these side effects, these agents also cause hypotension and syncopy, which tend to reduce mobility and thus delay rehabilitation and recovery of the spinal cord injured subjects. Further other side effects include constipation and rectal impaction which in tetraplegic subjects and paraplegic subjects with lesions above thoracic sixth vertebrae can paradoxically result in severe hypertension, a syndrome known as autonomic hyperreflexia.
This application further relates to new anesthetic and hypothermic agents, and more particularly to the use as general anesthetic and/or hypothermic agents, in mammals, of a previously known pharmacologic compound, guanabenz and certain of its related compounds (xe2x80x9cguanidino compoundsxe2x80x9d). When both properties, anesthesia and hypothermia are found in the same compound, its administration results in pseudo-hibernation, that results in a relatively bloodless operating field, which can be beneficial when undergoing major surgery. These guanidino compounds also have other valuable pharmocologic properties.
Guanabenz has long been used in clinical pharmacology, generally by oral administration, as an antihypertensive agent. It is known to be a stimulant, or agonist, of central alpha2-adrenergic receptors, resulting in a decrease of sympathetic outflow from the brain at the bulbar level to the peripheral circulatory system.
Among the known xe2x80x9cadverse effectsxe2x80x9d of guanabenz as an antihypertensive agent are sedation, anxiety, ataxia, depression, and sleep disturbances. Although most prior clinical use of guanabenz has involved oral administration, earlier parenteral testing in dogs had produced natriuresis, thus contraindicating long-term administration by this route for hypertension treatment.
Accidental oral overdosages of guanabenz, have not been reported to result in anesthesia; the incidents were recorded as hypotension, somnolence, lethargy, irritability, myosis and bradycardia in young children.
In U.S. Pat. No. 4,060,640, Kodama et al., described guanabenz, and its related compounds, as being central nervous system depressants that reduced hyperexcitability and induced sedation, thus overcoming psychic depression.
This alpha-adrenoceptor agonist has been shown to have a restorative effect on the central nervous system, especially in the treatment of motor and sensory functional losses due to the traumatic injury to the spinal cord (see U.S. Pat. No. 4,742,054).
I. Sensory-Motor Function Restoration
It is an object of the present invention to provide novel compounds which have the capability of restoring to a mammal maximal sensory-motor function following damage to the central nervous system caused by trauma or disease. It is a further object of the present invention to provide novel compounds having such capability but without undesirable side effects which would interfere with the treatment of any mammal having suffered traumatic central nervous system injury.
A further objective of the invention, the novel compounds are efficacious anti-spastic, or spasmolytic, agents that control spasticity caused as a result of neurological damage. These drugs would also produce little or no sedation or somnolence and would not drastically lower blood pressure.
II. Anesthesia and Hypothermia
Guanidino compounds, among the alpha-adrenergic receptor agonists, are capable of inducing profound anaesthesia and/or hypothermia in mammals, when administered in a sufficient unit dosage, i.e., at least about 3 mg/kg in rats and 0.05 mg/kg in primates. In order to expedite and render more efficient the onset of anesthesia, guanabenz is preferably administered intraperitoneally (I.P.), or intravenously (I.V.), in the usual liquid vehicles, e.g., preferably a 5% aqueous dextrose solution. The guanidino compound can be provided in any of the usual pharmaceutical forms, e.g., as a physiologically acceptable salt, such as guanabenz acetate, guanabenz HCl, guanabenz maleate, or guanabenz sodium succinate, dissolved in, e.g. a 5% aqueous dextrose solution. As guanabenz and others of these guanidino compounds are capable of passing through the blood-brain barrier, unlike many non-volatile anesthetics, they need not be administered intrathecally.
The term xe2x80x9cguanidino compoundsxe2x80x9d for both groups of activities includes any compound which has adrenergic receptor activity and which is sufficiently lipophilic to pass the blood-brain barrier in the central nervous system; and which include the moiety: 
in which xe2x80x9cnxe2x80x9d can be an integer from 1 to 3. The above moiety can be a branched acyclic group as shown above, or the atoms xe2x80x9ccxe2x80x9d, Na, xe2x80x9cNbxe2x80x9d, or xe2x80x9cNcxe2x80x9d can be part of a cyclic group, for example, an imidazolino, a benzimidazolino, a melamine (or triazine) group, an amino-1,3-diazacyclopentene-(2), aminocaffeine, an amino-1,3-diazacyclohexene-(2), or 3,5-Diamino-1,2,4-triazole.
This guanidino moiety can be part of a xanthine group, such as in 8-aminocaffeine, or a separate group linked with a xanthine group, such as by reacting a guanidino compound with theophylline-7-acetic acid, which product possesses alpha and beta adrenergic activity. When the moiety is combined with, i.e., 5-OH-tryptamine-3,4-dihydroxyacetaldhyde, gamma-aminobutyric acid, or choline, the resulting compound, in addition to alpha adrenoceptor activity, possesses serotonergic, dopaminergic, GABA-ergic, or cholinergic activities, respectively.
In the guanidino group of Formula I, above one of Na, Nb or Nc can be replaced with a sulfur or oxygen atom, i.e., xe2x80x94Sxe2x80x94, or xe2x80x94Oxe2x80x94, and also obtain the desired agonist activity. When one of Na, Nb or Nc is replaced by a carbon atom (xe2x80x94Cxe2x80x94), the resulting compound containing the group has an alpha-adrenergic antagonist activity, e.g., will reverse hypothermia or anesthesia induced by guanabenz, such as exemplified by compounds Nos. 96-101, 162, 163, 192, in Table I, below. These adrenergic antagonist compounds are also neuroprotective and, similar to guanidino compounds, possess glutamate (NMDA) receptor antagonistic activities.
In accordance with the first aspect of the present invention, there are provided pharmacologically active compounds having the capability of reestablishing previously nonfunctioning or dysfunctioning, or destroyed neurological functions in a traumatized or diseased mammal. These compounds comprise the reaction products of a guanidino, aminoguanidino, 2-imidazolino, 2-hydrazinoimidazolino, 2-guanidinobenzimidazolino, 3,5-diamino-1,2,4-triazole and the like groups with a methylated xanthine group, which provide a combination of receptor activity designed to stimulate appropriate receptors in the brain and spinal cord and thereby reestablish the lost negative feedback and thereby tonically stimulate sensory and motor neurons, in spite of a severely damaged central nervous system. These compounds are highly lipophilic and thus capable of crossing the blood/CNS barrier and they preferably have the following general formula: 
Wherein g and r can have a value of 0 or 1, to a total of one, h can be 0, 1 or 2, and n is 0 or an integer of at least 1 and preferably not greater than 2; the R groups can be hydrogen or non-interfering organic groups. R1 and R2 and R3 preferably include alkyl groups or hydrogen atoms, at least one of R1 and R2 and/or R3 most preferably comprising an alkyl group. R1 and/or R3 can be the bridging group to the guanidino moiety outside of the brackets, and can be an aliphatic group, saturated or unsaturated, preferably including a carboxyl group or a carbonyl group, oxygen, nitrogen, sulfur, connected to a nitrogen atom of the guanidino group by a double bond. Thus R1 and R3 can preferably include acetyl, acetaldehyde, propionyl, hydroxyalkyl. R4 and R5 can each be hydrogen, or any non-interfering organic group, preferably including lower alkyl, alkoxy, thioalkyl, alkenyl, aryl, aralkyl, or alkaryl or a nucleoside group, or any such group substituted with NH2, OH, OCH3, or halogen, sulfur, oxygen, or NO2. R6, if present, is a bridging group forming a closed heterocyclic ring compound with the two nitrogen atoms on the guanidino group, and can be any non-interfering organic group, which can include additional nitrogen atoms, halogen atoms, oxygen atoms, and can be aliphatic, cycloaliphatic, or aromatic, so as to form groups such as, e.g., imidazole, benzimidazole, triazine, thiopyrimidine, triazolethiol, diphenyl-2-imidazole-thiol.
The novel compounds of the present invention have an alpha2-adrenergic receptor agonist moiety and a beta-adrenoceptor agonist moiety. Preferably, the beta-receptor agonist moiety (within the brackets) is derived from a compound that has an indirect beta-adrenergic effect, such as the substituted xanthines, which enhance the metabolic effect of cyclic adenosine 3xe2x80x2,5xe2x80x2-monophosphate (c-AMP), by blocking c-AMP phosphodiesterase. These xanthines further enhance microcirculation within the muscle mass by increasing local vasodilation.
The present invention builds upon the effects noted in the earliest parent application hereto by combining in a single compound or complex the effects of the alpha2 and beta agonists.
As was noted during the earlier work, the previously known alpha2-adrenergic receptor agonists (xe2x80x9calpha2-agonistsxe2x80x9d), have other direct physiological effects on the mammal being treated, which often are contraindicated following trauma, such as spinal injury, e.g., the hypotensive effect of clonidine and guanabenz. It was recognized that such undesirable side effects can be counteracted by the simultaneous or sequential administration of an antagonist or a pressor agent, such as angiotensin II which could be titrated against the alpha2-agonist. Usually, it was extremely difficult to avoid any such hypotensive effect, or some time serious hypertensive effects. The compounds of the present invention, which include the guanidino, 2-amino-imidazolino, 2-hydrazino-imidazolino, 2-guanidinobenz-imidazolino, 3,5-Diamino-1,2,4-triazolino, or 2,3,5-s-triazine moiety, as the alpha2 agonist, plus a beta-agonist moiety, avoid severe hypotensive effect, and result in an improved reactivation and reestablishment of the descending monoaminergic pathways and ascending nociceptive pathways while also improving upon and speeding up the affirmative process of restoring motor and sensory functions to almost one/third of the time required by the alpha2 agonists.
The indirect beta-agonists, such as substituted xanthines, act by inhibiting the enzyme c-AMP phosphodiesterase, with the effect of increasing the ratio of c-AMP to c-GMP (cyclic guanosine-3xe2x80x2,5xe2x80x2-monophosphate). In addition, moieties derived from direct acting beta-agonist, such as 4-hydroxy-3-methoxymandelic acid, 3,4-dihydroxymandelic aldehyde, 3,4-dihydroxyphenyl(beta-hydroxy)-acetaldehyde may be combined through their aldehyde or carboxyl groups with guanidine, aminoguanidine, etc. to yield internally neutralized compounds which have similar effect.
Referring to Formula 1, the xanthine group is connected to the guanidino group through one of the guanidino-nitrogen atoms.
In addition, it has been found that similar effects can be obtained when in the guanidino moiety, one of the nitrogen atoms in the guanidino group shown in Formula 1 is replaced by a sulphur or an oxygen atom.
Typical species of this class of mixed agonist compounds are set out in the working examples below, as well by the following list:
A1. Guanidino-7-Acetyltheophylline
A2. 2-Guanidinobenzimidazolyl-7-Acetyltheophylline
A3. 3,4,5-Trimethoxybenzylidene-2-Hydrazinoimidazole
A4. 2-Hydrazinoimidazolyl-7-Acetyltheophylline
A5. Theobromine-1-Acetyl Guanidine
A6. Theophylline-7-Acetylamidoguanidine
A7. Theobromine-1-Acetylamidoguanidine
A8. Theophylline-7-Acetyliminoguanidine
A9. 2,4,6-Tris(7-Acetamidotheophylline)-1,3,5-s-Triazine
A10. 2,4-Bis(2,6-Dicholorbenzylideneimino)-6-(7-Acetamidotheophylline)-1,3,5-s-Triazine
A11. 2,4-Bis(1-Naphthylacetamido)-6-(7-Acetamidotheophylline)-1,3,5-s-Triazine
A12. 2,4-Bis(7-Acetamidotheophylline)-6-(2,6-Dichlorobenzyl-ideneamino)-1,3,5-s-Triazine
A13. Theophylline-7-Ethyleneiminoguanidine
Other such mixed agonist compounds are exemplified by the 8-amino caffeine compounds, such as cafaminol, or compounds numbered 191, 197, 203, 205, 209, 213-215 in Table II, below. In such compounds, the guanidino group, in part, is formed as part of the xanthine group by substituting an amino group onto the eighth position of the xanthine group. One method of preparing these compounds is shown in U.S. Pat. No. 3,094,531.
With mixed agonist or agonist-antagonist properties, the compounds of the present invention can be used as medicaments for mammals in the form of pharmaceutical preparations suitable for administration orally, parenterally, intraperitoneally, intravenously or as nasal spray. These compounds can be administered in a substantially pure form, with other active ingredients which may be desirable, or merely with a suitable pharmaceutical vehicle. The compounds are generally crystalline solids which may be at least partially soluble in commonly used organic salts. They are also generally soluble in liquid pharmaceutical vehicles, including water. Generally, the compounds can be formed as physiologically acceptable salts including the salts of inorganic acids, such as hydrochloric, hydriodic, sulfuric or phosphoric, as well as organic acids including acetic, malic, ethionic, malonic, citric, benzoic and pamoic. Generally, these acid addition salts are more soluble in water than the compounds per se. Formulation in a pharmaceutical vehicle can be carried out in accordance with techniques and in vehicles which are wholly conventional to those skilled in the art for the intended mode of administration.
For example, preparations for oral administration can be in either liquid or solid form, including for example syrups, elixirs, powders, capsules or tablets. The materials are preferably prepared for unit dosage form as powders which are preferably pressed into tablets or suitably encapsulated in, for example, conventional gelatine capsules. Any powders or compressed tablets can generally also comprise the usually suitable excipients and/or diluents, such as starch, lactose, stearic acid, magnesium stearate, dextrin or polyvinylpyrrolidone.
Other suitable solid carriers include magnesium stearate, sicaryl alcohol, talc, vegetable oils or fats, alcohols such an benzyl alcohols, gums, waxes, alkylene or polyalkylene glycols, such as propylene glycol or polypropylene glycol and any other well known carriers.
Suitable sterile solutions or suspensions can be prepared for parenteral or intraperitoneal administration, e.g., intravenous, containing for example water, physiological saline, benzyl alcohol, ethyl oleate, methylcellulose, dimethyl sulfoxide, polyethylene glycol liquid, as well as other liquid excipients well known in the pharmaceutical or veterinary art. Other auxiliary pharmaceutical materials which can be present include preservatives, stabilizers, wetting or emulsifying agents, or osmotic salts or buffering agents, as is well known to the pharmaceutical or veterinary art. As these formulations are generally well known and conventional, more specific instructions need not be presented for purposes of defining this invention.
As stated, the mixed alpha/beta receptor active compounds of the present invention are most effective in treating the undesirable after-effects of traumatic spinal injury, including even transection of spinal cord. Restoration of at least some normal sensory and motor control can be obtained as a result of treatment, especially if carried out within a relatively short time after injury to the spinal cord.
Because the compounds of the present invention do not have many of the undesirable side effects of utilizing the prior alpha2-adrenoreceptor agonists of the parent application, it is not necessary to postpone treatment using these novel compounds until after stabilization of the vital signs and recovery from the initial shock. Indeed, many of these compounds are also effective in treating the initial shock conditions by way of stabilizing or even slightly elevating arterial blood pressure and improving microprofusion pressure in the area of injury. Thus, the compounds of the present invention have positive hemodynamic effect as well as positive neurological effects.
In all cases, as explained in the earlier work, it is necessary to insure, by taking active surgical steps, if necessary, to remove any mechanical obstruction and compression pressure as created by crushed bone, growth of scar tissue or connective tissue or any other mechanical cause, especially in chronic spinal cord injured mammals.
The mixed agonists of this invention also have been found to interfere with the,formation of undesirable scar tissue at the trauma site. It is believed that these mixed agonists interfere with triple helix formation in the synthesis of collagen protein, thus preventing or reducing the formation of hard scar tissue at the trauma site.
During treatment using the compounds of the present invention, it is greatly preferred that the plasma level of the compound in the blood stream of the mammal being treated be maintained as constant as feasible. This is especially important with respect to spinal injuries in order to reduce or substantially eliminate autonomic dysreflexia and spasticity during treatment until permanent return of sensory and motor function has been obtained. These compounds generally should be administered in a proportion of at least about 10 mcg/kg of body weight, and preferably in an amount of at least 15 mcg and preferably not more than about 100 mcg/kg of body weight, and most preferably not more than about 70 mcg/kg of body weight. However, it has been found that the optimal proportion in the blood is not directly proportional to body weight, but rather to a combination of factors including body weight and body superficial area.
It may be preferable to administer these novel pharmacological agents using a sustained release form, for example, the conventionally available sustained release capsules or sustained release transdermal products. Alternatively, if it is not feasible to utilize the sustained release forms, these novel compounds can be administered regularly at relatively short intervals, for example, 2 to 4 times per day. Although not as desirable for chronic long-term treatment, these compounds can, at least initially after the trauma, be administered intraperitoneally or intravenously to maintain a constant, tonic effect by slow administration of medication, or as a single injection, at intervals.
An additional effect of the present novel compounds, especially important in the immediate aftermath of traumatic injury and shock, is the immediate stimulation of spinal cord motor neurons, which keeps the muscle mass from wasting, preventing loss of weight and demineralization of the skeleton, all of which are common occurrences after spinal cord trauma. In addition, by avoiding constipation, as is often caused by pure alpha2 agonists, extreme hypertension and autonomic hyperreflexia are also avoided. Further, since the compounds are relatively internally neutralized with respect to c-AMP and c-GMP, receptor supersensitivity will be greatly minimized.
Most of the novel compounds of the present invention in accordance with Formula IA above, can be prepared by reacting a first compound (xe2x80x9cAxe2x80x9d) which contains a guanidino group and which can be present as part of a heterocyclic group, e.g., an amino triazine group, an amino arylimidazole, an amino benzylimidazole, or an aminoimidazoline group, or an equivalent thio compound where one of the nitrogen atoms forming any of the above groups is replaced by a sulphur atom, with a second compound (xe2x80x9cBxe2x80x9d) comprising a direct or indirect beta-adrenergic receptor agonist, such as a substituted xanthine or analogs of beta-hydroxyphenyl acetic acid, aldehyde or amine. Each of the above A and B compounds preferably include one of a carbonyl group (such as a carboxyl group or an aldehyde group), a hydroxyl group or an amino (xe2x80x94NH2), which are mutually reactive. Most preferably, the xe2x80x9cAxe2x80x9d compound reacts through a primary or secondary amino nitrogen atom forming part of the guanidino or aminoguanidino moiety.
Suitable group A compounds include guanidine, aminoguanidine, 2-guanidinobenz imidazole, 2-amino-imidazole, 2-aminodihydrothiazine, 2-hydrazinoimidazoline, 2,4,6-triamino-1,3,5-s-triazine, 2,4-diamino-6-phenyl-1,3,5-s-triazine, 2,4-bis(diethylamino)-6-hydrazino-1,3,5-s-triazine, 4-methyl-4H-1,2,4-triazole-3-thiole, 4,5,diphenyl-2-imidazole-thiole, 2-(4-aminophenyl-6-methyl-benzothiazole), 3,5-diamino-1,2,4-triazole, 8-aminocaffeine and their acid addition salts. The 8-aminocaffeine compound can be prepared, e.g., by reacting 8-chlorocaffeine with ammonia.
Useful B group compounds which are preferably direct or indirect beta-agonists, can be, for example, theophylline, etofylline, theophylline-7-acetic acid, theophylline-7-acetaldehyde, 7-(2,3-dihydroxy)-propyltheophylline, 1-theobromine acetic acid, 1-theobromine acetaldehyde. Alternatively, 8-chlorocaffeine can be reacted with compounds having a free amino-group, to form the third leg of the guanidino group, or to form a bi-guanide by reacting 8-chlorocaffeine with, e.g., aminoguanidine, or 2-hydrazinoimidazole.